a) Field of the Invention
This invention relates to a multiplate lockup clutch useful primarily as a torque transmitting device in a vehicle and also to a torque converter with the multiplate lockup clutch incorporated therein. More specifically, the present invention is concerned with improvements in or relating to friction plates for multiplate lockup clutches.
b) Description of the Related Art
A multiplate lockup clutch, which performs transmission or non-transmission of torque, is generally arranged in a torque converter which is in turn disposed together with an automatic transmission or the like in a vehicle to transmit torque. An illustrative torque converter with such a multiplate lockup clutch incorporated herein is shown in FIG. 8.
A torque converter 1 is constructed of a multiplate lockup clutch 2, a damper 3, a pump impeller 4, a turbine runner 5, and a stator 6. The stator 6 is supported at axially opposite sides thereof by needle bearings 7 and 8, respectively, and on an inner circumference of the stator 6, an unillustrated one-way clutch is arranged to prevent rotations in a direction reverse to a predetermined direction.
In the multiplate lockup clutch 2, separator plates 24 and a backing plate 25, all of which are spline-fitted on an inner circumference of a clutch case 23, and friction plates 50, which are spline-fitted on an outer circumference of a hub 22, are alternately arranged and are supported by a snap ring 26. On a left side of these plates as viewed in the drawing, a piston 21 is arranged. The multiplate lockup clutch 2 is designed such that, when pressure oil is supplied into a pressure oil compartment 27, the piston 21 is caused to move rightward as viewed in the drawing and hence, the separator plates 24, friction plates 50 and the backing plate 25 are held between the piston 21 and the snap ring 26 to obtain an engaged state.
FIG. 9 is a front view of one of conventional friction plates 50 employed in a multiplate lockup clutch useful in a torque converter of the above-mentioned construction. The friction plate 50 has a construction that a friction lining 51 is secured on a ring-shaped core plate 52 with splines 53 arranged on an inner circumference thereof. On the friction lining 51, communicating grooves 54 are formed such that an inner circumferential edge and an outer circumferential edge of the friction plate 50 are communicated with each other through the communicating grooves 54. These communicating grooves 54 are arranged to damp or reduce judder.
Now, referring back to FIG. 8, the pump impeller 4 is normally kept rotating because it is directly connected to an engine (not shown) via a connecting part 10. A certain level of hydraulic pressure, therefore, normally exists so that, even while the piston 21 of the multiplate lockup clutch 2 is out of operation, a slight pressure is exerted from a right side of the drawing (in a direction of arrows in FIG. 8), in other words, from a side of the backing plate 25. Under this pressure, the backing plate 25, the friction plates 50 and the separator plates 24 are pressed against the piston 21 and hence, are brought into engagement, whereby drag torque is produced. Further, the communicating grooves 54 which are arranged to damp judder show high oil discharge performance, and tend to delicately respond to the above-mentioned pressure and to increase the drag torque further.
An object of the present invention is, therefore, to provide a multiplate lockup clutch reduced in the above-mentioned drag torque which is produced by an internal pressure of a torque converter. Another object of the present invention is to provide a torque converter with the multiplate lockup clutch incorporated therein.
In a first aspect of the present invention, there is thus provided a multiplate lockup clutch for use in fluid, said multiplate lockup clutch being provided with a multiplicity of friction plates, wherein each of the friction plates is provided on a friction surface thereof with at least one combined groove; and the combined groove consists of a first groove, which extends from an inner circumferential edge to an outer circumferential edge of the friction plate and communicates an inner circumference and an outer circumference of the friction plate with each other, and a second groove which intersects the first groove and extends in a circumferential direction of the friction plate. The multiplate lockup clutch has an advantageous effect in that formation of an oil on each friction plate is facilitated to reduce drag torque to be produced by an internal pressure of a torque converter. Each of the friction plates may preferably be provided with a plurality of such combined grooves. These combined grooves may preferably be repetitively formed at predetermined intervals in the circumferential direction of the friction plate.
In a second aspect of the present invention, there is also provided a multiplate lockup clutch useful in fluid, said multiplate lockup clutch being provided with a multiplicity of friction plates, wherein each of the friction plates is shaped in a waveform as viewed in a circumferential direction thereof. Formation of an oil on each friction plate is facilitated and, when the multiplate lockup clutch is brought into engagement under an internal pressure of a torque converter, each friction plate is brought only at crest portions thereof into engagement with its associated separator plate, leading to a reduction in the contact area between the friction plate and its associated separator plate. The multiplate lockup clutch, therefore, has an advantageous effect that the drag torque to be produced by the internal pressure is reduced further. The waveform may preferably be formed such that crest portions and trough portions are alternately arranged in the circumferential direction of the friction plate.
In third and fourth aspects of the present invention, there are also provided torque converters with multiplate lockup clutches incorporated therein, respectively. These multiplate lockup clutches are the same as those described above as the first and second aspects of the present invention, respectively. These torque converters can show the advantageous effects of the corresponding multiplate lockup clutches.